Merge pull request #1746 from realm/jas/backlink-update

Initial work for unnamed backlink queries and backlink count

docs/tutorials/query-language.md

@@ -95,3 +95,21 @@ Example:
 // Find contacts with friends above 21 in SF
 let teens = realm.objects('Contact').filtered('SUBQUERY(friends, $friend, $friend.age > 21 AND $friend.city = "SF").@count > 0');
 ```
+
+### Backlink queries
+
+Other objects can link to an object and you can query on that releationship using the `@links` and `@links.ClassName.PropertyName` syntax.
+If the relationship of the LinkingObject is named, use the name in the query just like you would use any other property for readability.
+If the relationship is not named, you can use the `@links.ClassName.PropertyName` syntax where `ClassName.PropertyName` describes the forward relationship.
+
+Example:
+```JS
+// Find contacts where someone from SF has them as friends
+realm.objects('Contact').filtered('@links.Contact.friends.city == "SF"');
+
+// Find contacts with no incomming links (across all linked properties)
+let isolated = realm.objects('Contact').filtered('@links.@count == 0');
+
+// Find contacts with no incoming friend links
+let lonely = realm.objects('Contact').filtered('@links.Contact.friends.@count == 0');
+```

src/js_results.hpp

@@ -160,8 +160,7 @@ inline void alias_backlinks(parser::KeyPathMapping &mapping, const realm::Shared
             if (property.type == realm::PropertyType::LinkingObjects) {
                 auto target_object_schema = schema.find(property.object_type);
                 const TableRef table = ObjectStore::table_for_object_type(realm->read_group(), it->name);
-                const TableRef target_table = ObjectStore::table_for_object_type(realm->read_group(), target_object_schema->name);
-                std::string native_name = "@links." + std::string(target_table->get_name()) + "." + property.link_origin_property_name;
+                std::string native_name = "@links." + target_object_schema->name + "." + property.link_origin_property_name;
                 mapping.add_mapping(table, property.name, native_name);
             }
         }
@@ -181,6 +180,7 @@ typename T::Object ResultsClass<T>::create_filtered(ContextType ctx, const U &co
     auto const &object_schema = collection.get_object_schema();
     DescriptorOrdering ordering;
     parser::KeyPathMapping mapping;
+    mapping.set_backlink_class_prefix(ObjectStore::table_name_for_object_type(""));
     alias_backlinks(mapping, realm);
 
     parser::ParserResult result = parser::parse(query_string);

tests/js/linkingobjects-tests.js

@@ -109,11 +109,13 @@ module.exports = {
             let english = realm.create('Language', {name: 'English'});
             let french = realm.create('Language', {name: 'French'});
             let danish = realm.create('Language', {name: 'Danish'});
+            let latin = realm.create('Language', {name: 'Latin'});
             let canada = realm.create('Country', {name: 'Canada', languages: [english, french]});
             let denmark = realm.create('Country', {name: 'Denmark', languages: [danish, english]});
             let france = realm.create('Country', {name: 'France', languages: [french, english]});
         });
         let languages = realm.objects('Language');
+        {
             let spokenInThreeCountries = languages.filtered('spokenIn.@count == 3');
             TestCase.assertEqual(spokenInThreeCountries.length, 1);
             TestCase.assertEqual(spokenInThreeCountries[0].name, 'English');
@@ -127,6 +129,29 @@ module.exports = {
             TestCase.assertEqual(languagesSpokenInCanada.length, 2);
             TestCase.assertEqual(languagesSpokenInCanada[0].name, 'English');
             TestCase.assertEqual(languagesSpokenInCanada[1].name, 'French');
+        }
+        // check the same but using the unnamed relationship which is available to users
+        {
+            let spokenInThreeCountries = languages.filtered('@links.Country.languages.@count == 3');
+            TestCase.assertEqual(spokenInThreeCountries.length, 1);
+            TestCase.assertEqual(spokenInThreeCountries[0].name, 'English');
+            let spokenInTwoCountries = languages.filtered('@links.Country.languages.@count == 2');
+            TestCase.assertEqual(spokenInTwoCountries.length, 1);
+            TestCase.assertEqual(spokenInTwoCountries[0].name, 'French')
+            let spokenInOneCountry = languages.filtered('@links.Country.languages.@count == 1');
+            TestCase.assertEqual(spokenInOneCountry.length, 1);
+            TestCase.assertEqual(spokenInOneCountry[0].name, 'Danish')
+            let languagesSpokenInCanada = languages.filtered('@links.Country.languages.name ==[c] "canada"');
+            TestCase.assertEqual(languagesSpokenInCanada.length, 2);
+            TestCase.assertEqual(languagesSpokenInCanada[0].name, 'English');
+            TestCase.assertEqual(languagesSpokenInCanada[1].name, 'French');
+        }
+        let notSpokenInAnyCountry = languages.filtered('@links.@count == 0'); // no incoming links over any relationships to the object
+        TestCase.assertEqual(notSpokenInAnyCountry.length, 1);
+        TestCase.assertEqual(notSpokenInAnyCountry[0].name, 'Latin');
+        let notSpokenMethod2 = languages.filtered('@links.Country.languages.@count == 0'); // links of a specific relationship are 0
+        TestCase.assertEqual(notSpokenMethod2.length, 1);
+        TestCase.assertEqual(notSpokenMethod2[0].name, 'Latin');
     },
 
     testMethod: function() {